Protect steel from rust with anti corrosion coating

The estimated global cost of metal corrosion is trillions of pounds. Corrosion is caused by a chemical reaction between a metal and its environment, typically producing an oxide or a salt of the original metal. The long and the short of it is: the metal is weakened, and so is the structure it creates. The good news is, a lot of this loss can be prevented by being proactive, and choosing the right anti corrosion coating from the start.

Anti corrosion coating acts as a barrier between the metal and its environment, increasing its durability and lifespan.

Whether corrosion is due to moisture, chemicals, salt spray, or oxidation, corrosion resistant coatings for steel and metal can help protect the substrate from the elements.

Types of corrosion treatable with anti corrosion coating

Which anti corrosion coating you choose depends on the substrate material, the intended use of the material, as well as its intended environment and performance levels. Whether there will be a need for on-site treatment or whether it is strictly a shop treatment is also an important factor. For smaller jobs such as a rusting car or bike, all you may need is an anti rust spray. Some of the worst culprits for metal corrosion are:

Galvanic – Triggered when two metals of different electrochemical potentials come into electrical (or physical) contact in presence of an electrolyte, such as saltwater. Current flows through the electrolyte from one metal to the other (the anode to the cathode), and the anode will corrode.

Pitting – Pits or cavities form in the surface of a metal, caused by non-uniformities.

Crevice – Caused by liquids stagnating within a crevice, crack or seam, causing a chemical change and so, corrosion.

Exfoliation – Also known as layer corrosion. Metal corrodes from within, forcing the layers apart like they are peeling.

Types of anti corrosion coating and solutions

One of the most important principles of metal coatings is cathodic protection. Cathodic protection is a method of preventing galvanic corrosion by providing a more easily corroded metal (such as zinc) to be the anode to the protected metal’s cathode. Also called the sacrificial anode, this metal will corrode instead of the protected metal.

Hot dip galvanising is done in a bath of molten zinc.

The two most common methods for applying a metal anti corrosion coating are hot dip galvanisation and thermal (metal) coating:

Hot Dip Galvanisation is the process of immersing a metal in a bath of molten zinc, allowing the zinc to bond to the substrate and form an alloy coating, which is then coated in zinc as it is removed from the bath. Galvanising uses the principle of cathodic protection, as the zinc coating acts as an anode to its substrate.

Thermal (metal) spraying applies zinc or aluminium to a substrate by taking the metal in the form of a powder or wire and feeding it into a special spray gun. There the metal is melted and can be sprayed onto the substrate. It does not alloy, but instead works by coating the surface in overlapping metal platelets.

Anti corrosion paint and powder coating:

Paints consist of three main ingredients:

Binders (resins, from which the paint gets its name)

Pigments (which provide the anti corrosion properties)

Solvents

The combination of the adhesive power of the binder and the corrosion-inhibiting pigments is what makes these coatings so effective. Anti corrosion coatings are available as metal-rich paints, polymer-based paints such as polyurethane, as well as powder coating, and can be divided into three categories:

Barrier coatings – non-porous coating designed to prevent corrosive factors coming into contact with the substrate

Inhibitor coatings – release a chemical which interferes with the electrolyte and stops the corrosion process

Galvanic coatings – metal-rich coatings which provide a sacrificial layer or use the principle of cathodic protection to prevent corrosion.

When hot dip galvanisation is used together with a topcoat of anti corrosion paint or powder it is known as a Duplex System. It provides multiple types of protection and the longest-lasting results.

Proper anti corrosion coating for steel is a multi layer system

Like all coatings solutions, the condition of the substrate for anti-rust coatings is paramount. For proper adherence of any coating, it needs to be clean and clear of dirt, debris and, depending on the coating, rust. For an anti corrosion treatment to coat steel, the basic process is:

Intermediate coat (there may be several. Build the thickness and protection of the coating)

Finishing coat (provides appearance and surface resistance, often first line of defence)

Each layer needs to be compatible in order for the system to work effectively.

The best anti corrosion coating for the job

Which anti corrosion paint you choose will depend on your substrate, the conditions it will need protection from, the degree of use and just how long-lasting you want it to be.

Epoxy: Epoxy resins are tough and abrasion resistant. They have excellent corrosion resistance to most of chemicals and solvents. Epoxy coatings are not resistant to UV radiation.

Coal tar epoxies: This is an epoxy-containing coal tar, so it comes in black or brown. Coal tar epoxy is good for underwater structures as it provides excellent waterproofing.

Polyurethane: Polyurethanes make excellent corrosion resistant paints. They are not affected by UV light, so they are preferred over epoxy resins for all exterior applications.

Chloro-rubber paints: They provide an excellent corrosion resistant coating in a chemical environment. However, they are easily corroded by solvents and cannot withstand high temperatures.

Fluoropolymers: Possibly better known for their non-stick abilities (think Teflon), these polymers are also desirable for their anti abrasion and anti corrosion properties. They also have the benefit of being able to withstand high temperatures.

Anti corrosion coating products & prices UK

Different coating processes use different methods to calculate cost. Hot dip galvanising prices are usually calculated by weight. The galvaniser will quote a price per tonne, and then use the weight of your steelwork after galvanising to calculate the final cost. Unlike galvanising, powder coating prices tend to be calculated by size or surface area. Regional differences in materials, labor and equipment can all have an impact on overall costs when contracting a coating expert. If you are looking for local manufacturers and prices in the UK, we recommend you request a quote.

Here is a selection of products on the market to give you a rough guide as to the cost of anti corrosion paint:

Product

Coating type

Price (RRP)

Packaging

Jotun Jotamastic 90

Epoxy coating for above and below water, on concrete or steel, with abrasion and chemical resistance.

£199.95

20 L

Jotun Barrier 90

Zinc-rich epoxy containing 90% zinc. Suitable for above water and on steel, with abrasion and water resistance.

£159.95

8.75L

Rust-Oleum Mathys Noxyde

Water-based paint, for use above water on metal, roofing and cladding. UV and abrasion resistant.

£158.16

20Kg

Rust-Oleum Combi Primer

Matt finish primer for use on new or slightly rusted surfaces.

£14.44

750ml

A final guide: The international standard for corrosion

Anti corrosion coatings are of vital importance to our daily lives. The steel structures that surround us, such as bridges, will weaken and possibly collapse without protection from rust and corrosion. This is why there is an international standard for corrosion protection of steel structures by protective paint systems, called ISO 12944. The standard provides guidelines for dealing with corrosive environments, and the appropriate measures to take for each.

Following these guidelines will allow you to pick appropriate anti corrosion coatings, allowing you to avoid overspending on unnecessary degrees of protection or simply making the wrong choice.

ISO 12944 divides corrosive environments into five main groups, labeled C1-C5, ranging from a low corrosive environment to a high one. A C1 environment is a heated building or rural area with low pollution, while a C5 environment is either C5I (Industrial) or C5M (Marine), environment with the highest corrosive factors. Once you have identified your environment, you can identify the right coating systems for your project and the right anti corrosive paint specification to protect it for years to come.

If you would like more information about anti corrosion coatings and where to find them, please get in touch. We are happy to help!

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